1. Field of the Invention
The present invention relates to a conductive composition containing a π conjugated conductive polymer and production method thereof. The present invention further relates to an antistatic coating material for imparting antistatic properties to a film, an antistatic coating material having antistatic properties, an antistatic film used in wrapping materials of food and electronic parts, an optical filter used for the front surface of a liquid crystal display and a plasma display, and an optical information recording medium, such as CDs and DVDs. The present invention relates to capacitors such as an aluminum electrolytic capacitor, tantalum electrolytic capacitor, and niobium electrolytic capacitor and a production method thereof.
2. Description of Related Art
π conjugated conductive polymers are known as organic conductive materials. The π conjugated conductive polymers is generally referred to an organic polymer composed of the main chain of a conjugated system, and examples of the π conjugated conductive polymers include polypyrroles, polythiophenes, polyacetylenes, polyphenylenes, polyphenylene vinylenes, polyanilines, polyacenes, polythiophene vinylenes, and copolymers thereof. These π conjugated conductive polymers are usually synthesized by an electrolytic polymerization method or a chemical oxidative polymerization method.
In the electrolytic polymerization method, a previously prepared base such as an electrode material is immersed in a mixed solution of an electrolyte as a dopant and precursor monomers for constituting a π conjugated conductive polymer to form a film of the π conjugated conductive polymer on the base. Therefore, mass production is very difficult.
On the other hand, there are no such limitations on the chemical oxidative polymerization method. A large amount of a π conjugated conductive polymer can be produced in a solution by adding oxidant and oxidation polymerization catalysis to precursor monomers of the π conjugated conductive polymer.
However, the π conjugated conductive polymer is obtained as an insoluble solid powder in the chemical oxidative polymerization method because the polymer becomes less soluble in a solvent as the conjugated system of the main chain of the polymer grows. It is difficult to form a uniform film of a π conjugated conductive polymer on a base surface if the polymer is insoluble. Additionally, the π conjugated conductive polymer tends to be an amorphous block and then a conductive composition containing the π conjugated conductive polymer has low conductivity.
Therefore, some methods to solubilize the π conjugated conductive polymers have been attempted. They are a method of introducing a functional group into the polymers, a method of dispersing the polymers in a binder resin, and a method of adding an anion group-containing polymeric acid to the polymer.
For example, a method of preparing an aqueous solution of poly(3,4-dialkoxythiophene) by the chemical oxidative polymerization of 3,4-dialkoxythiophene using oxidant in the presence of polystyrene sulfonic acid, which is an anion group-containing polymeric acid having a molecular weight of 2000 to 500000, in order to improve the dispersibility in water, is disclosed in Japanese Patent Publication No. 2636968. A method of preparing an aqueous colloid solution of a π conjugated conductive polymer by chemical oxidative polymerization of a precursor monomer of the polymer in the presence of polyacrylic acid, is disclosed in Japanese Unexamined Patent Application, First Publication No. 7-165892.
According to methods disclosed in Japanese Patent Publication No. 2636968 and Japanese Unexamined Patent Application, First Publication No. 7-165892, an aqueous dispersion solution containing a π conjugated conductive polymer can be easily prepared. These methods require a π conjugated conductive polymer to contain a large amount of anion group-containing polymeric acid for ensuring its dispersibility. Therefore, the problem occurs that the obtained conductive compositions contain a large amount of compounds which do not contribute to conductivity, making it difficult to achieve high conductivity.
In the chemical oxidative polymerization method, high oxidative oxidants cause unfavorable side reactions in high probability during chemical oxidative polymerization. Therefore, polymer structures having poor conjugated properties may be produced, the produced polymer may be excessively oxidized, or impurity ions may remain in the obtained polymer, causing low conductivity and long-term stability of the obtained π conjugated conductive polymer. In addition, since the π conjugated conductive polymer is a highly oxidized state, it is considered that radicals will be formed by oxidative degradation of a portion of the polymer due to the external environment such as heat, and then degradation progresses according to a radical chain reaction.
Resin films themselves are insulators and easily electrically charged. Furthermore, resin films tend to charge static electricity by friction or the like. Moreover, static electricity is not easily removed, but rather accumulates causing various problems.
Particularly, when a resin film is used for food packaging material emphasizing sanitary properties, dust and dirt are absorbed in display, the appearance is significantly impaired and in some cases the commodity value is lowered. When resin film is used for packaging a powder, charged powder is absorbed or repulsed in its packaging or use, and therefore causes the inconvenience that handling of the powder becomes difficult. When a precision electronic part is packaged with a resin film, it is a feared that the precision electronic part is damaged by the static electricity; therefore, the occurrence of static electricity must always be prevented.
Moreover, it is desirable that the surface of an optical filter or an optical information recording medium has high hardness and high transparency as well as antistatic properties to prevent the adherence of dust and dirt due to the static electricity. Particularly, it is desired that the surface resistance of the antistatic property be in the region of about 106 to 1010Ω and that the resistance stabilizes (i.e., stabilized antistatic properties), from which antistatic coating having antistatic properties and high hardness is provided on the surface of optical filter or optical information recording medium. In order to impart antistatic properties, for example, a method for coating a resin film or a surfactant on the surface and a method for kneading a surfactant into a resin forming a resin film or an antistatic coating have been adopted (for example, see “Fine Chemical Antistatic Agents Latest Market Trend (the first volume),” Vol. 16, No. 15, 1987, p. 24-36, published by CMC).
However, electrostatic prevention based on this surfactant has the drawback that its conduction mechanism is one of ion conduction, therefore, it is easily affected by humidity, conductivity increases by high humidity; however, conductivity decreases by low humidity. Therefore, the antistatic function deteriorates and antistatic performance is not displayed as necessary in an environment where the humidity is low, and especially static electricity easily occurs.
If a metal or carbon with electron conduction as conduction mechanism is used, such humidity dependence disappears, but these materials are totally opaque and not applicable for purposes requiring the transparency.
Moreover, a metal oxide such as ITO (Indium Tin Oxide) has transparency and adopts the electron conduction as a conduction mechanism; therefore, it is suited in this respect, but a process using a sputtering apparatus must used for its film-forming Not only is the process complicated but also the manufacturing cost rises. A coating film of inorganic metal oxide has low flexibility. When a film is formed on a thin base film, the coating film may be broken and does not exhibit conductivity. In addition, it is feared that peeling occurs at the interface and the transparency reduces because the adhesion to the base being an organic substance is low.
Moreover, π conjugated conductive polymers are known as organic materials with electron conduction as the conduction mechanism, but the π conjugated conductive polymers generally have insoluble and infusible properties, and it is difficult to coat the polymers on a base film after polymerization. Accordingly, it has been attempted that aniline be polymerized in the presence of a polymeric acid with a sulfo group (polyanion) to form a water-soluble polyaniline, the obtained mixture is used, coated on a base film and then dried (e.g., see Japanese Unexamined Patent Application, First Publication No. 1-254764).
However, as with the method described in Japanese Unexamined Patent Application, First Publication No. 1-254764, if aniline is directly polymerized on a base, an antistatic coating can be formed. In this case, the antistatic coating has low conductivity because the coating is not obtained by a π conjugated conductive homopolymer, and the adhesion to a resin base is low and manufacturing processes are also complicated because the antistatic coating is water-soluble.
Capacitors are given as example of using the π conjugated conductive polymers.
In recent years, it has been required to reduce the impedance of capacitors used for electronics in a high-frequency region with the digitalization of electronics. A so-called functional capacitor in which an oxide film of valve metals such as aluminum, tantalum, and niobium is adopted as a dielectric and a π conjugated conductive polymer is formed on this surface and used as a cathode and thus far has been used in response to this requirement.
As shown in Japanese Unexamined Patent Application, First Publication No. 2003-37024, it is general that the structure of this functional capacitor has an anode consisting of a porous valve metal body, a dielectric layer formed by oxidizing the surface of anode, and a cathode obtained by laminating a solid electrolyte layer, a carbon layer and a silver layer on the dielectric layer. The solid electrolyte layer of the capacitor is a layer constructed from a π conjugated conductive polymer of pyrrole, thiophene, and the like, and the layer performs to penetrate into the inside of porous body, come into contact with a larger area of electrolyte layer to derive a high capacity, restore defects of the dielectric layer, and prevent leakage of a current.
An electrolytic polymerization method (see Japanese Unexamined Patent Application, First Publication No. 63-158829) and a chemical oxidative polymerization method (see Japanese Unexamined Patent Application, First Publication No. 63-173313) have been widely known as methods for forming the π conjugated conductive polymers.
However, the electrolytic polymerization method has the problem that a conductive layer made of manganese oxide must be formed on the surface of the porous valve metal body beforehand, the process is complicated, and further the manganese oxide has low conductivity and weakens the effect of using the π conjugated conductive polymers having high conductivity.
The chemical oxidative polymerization method has the problem that the polymerization time is long, the polymerization must be repeated to ensure the thickness, the production efficiency of capacitors is low and the conductivity is also low.
Accordingly, a method wherein conductive polymers are not formed by the electrolytic polymerization method and the chemical oxidative polymerization method (see Japanese Unexamined Patent Application, First Publication No. 7-105718) has been proposed. A method comprising the steps of polymerizing aniline while allowing a polymeric acid with a sulfo group or carboxy group to coexist to prepare a water-soluble polyaniline, applying the aqueous solution of polyaniline on a dielectric layer, and then drying has been described in Japanese Unexamined Patent Application, First Publication No. 7-105718. This method is simple, but the permeability for the inside of porous body of the polyaniline solution deteriorates, the conductivity is low because the polymeric acid other than the π conjugated conductive polymer is contained and the humidity dependence on conductivity by the effect of polymeric acid may also be observed.
A capacitor having a low equivalent series resistance (ESR) as index of impedance has been desired, and the conductivity of the solid electrolyte layer must be increased to decrease ESR. As a method for increasing the conductivity of the solid electrolyte layer, for example, it has been proposed to highly control conditions for the chemical oxidative polymerization method (see Japanese Unexamined Patent Application, First Publication No. 11-74157). However, in the production method, the complex chemical oxidative polymerization method is more complicated in many cases, thus the simplification and low costing of processes cannot be realized.